It may be necessary for various reasons in exhaust systems of internal combustion engines to inject a liquid educt into the exhaust gas stream. For example, fuel may be injected into the exhaust gas stream upstream of an oxidation catalyst in order to induce an exothermal combustion reaction at an oxidation catalyst arranged downstream. For example, a reducing agent, e.g., ammonia, may likewise also be injected into the exhaust gas stream in order to reduce nitrogen oxides being carried by the exhaust gas in an SCR catalyst arranged downstream. Instead of ammonia, urea or an aqueous urea solution may also be injected into the exhaust gas stream. Ammonia and water will then form from the urea-water solution by a hydrolysis reaction. Furthermore, a fuel or another suitable reducing agent may be injected into the exhaust gas stream upstream of an NOx storage catalyst in order to regenerate the NOx storage catalyst.
To improve or make possible the mode of action of the educt injected in the liquid form into the exhaust gas line, extensive evaporation is just as desirable as a thorough mixing with the exhaust gas in order to thus obtain the most homogeneous exhaust gas-educt mixture possible. The exhaust system may be equipped for this with a mixing and/or evaporating device arranged in the exhaust gas line downstream of the injection means.
Depending on the injection means used, the educt may be introduced in the form of a liquid jet, which flares up in a conical shape. Low exhaust gas temperatures and low flow velocities prevail at low engine loads and exhaust gas temperatures. The liquid jet can subsequently impact on a corresponding structure of the mixing and/or evaporating device. Depending on the design of the mixing and/or evaporating device, the liquid jet may pass through the particular structure of the mixing and/or evaporating device at least partially and then reach in the liquid form an exhaust gas treatment means, at which the injected liquid shall only arrive in the form of the most homogeneous gas mixture possible. The consequence is a reduced mode of action as well the risk of damage.